New ACP web item: "Live" SkyChart with telescope position for ACP Web UI

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In these days of endless bad weather, I've had some time to play around with programming & learning some new things (started from zero when I got ACP last year). I've never done jscript before, & had a peek at different parts of ACP to figure out how to use it.
Since I'm often checking my imaging-progress from my phone, I often wonder where my scope is pointing, & how far from the meridian I am... Sure, the alt / az info is all there, but since I'm pretty new in astronomy, I prefer to have it all on a nice sky-map in front of me. That's not a problem when using a computer, but when I'm on my phone, I often wish for more.

So I decided to try & make a new tiddler for the ACP Web UI, namely a chart of the current sky above my observatory, & also a reticle where my scope is pointint. After countless of hours, the "beta" is available if you want to try it out.

Here's an example from today, when tracking Castor, and scope-reticle showed correct position by using alt/az from the scope.
(Click image for bigger version)

First off, I went to http://www.fourmilab.ch/cgi-bin/Yoursky to generate a reusable image-url for my location, to be used inside the tiddler.
Then I googled around for hours, figuring out how to convert the scope alt/az into coordinates for a reticle on top of the sky-chart image. After a while I found the formula for Polar to Cartesian conversion, & how to implement them in Jscript. It took me a while to realize jscript uses radians instead of degrees when using the sin/cos functions, but I finally figured out how to overcome that too... I dissected a few ACP .asp to figure out how to create my own first .asp. I had great fun learning tons of new stuff about programming, especially since it's my first go at jscript.

The chart generated online have some weird non-linear geometry I haven't figured out yet, the distance between altitude-circles (let's say 10°. 20°, 30°) isn't constant in the image like I would've thought, it missed the target with up to 10 degrees in the beginning, so I had to throw in a compensating formula (which isn't anywhere exact since I never put time into understanding the geometric "distortion" in the generated image... But I think my hipshot-formula does a pretty ok job now, the target stars always ends up close to the center of the reticle every time, so that's good enough for me.

I've also created two transparent overlays that goes on top of the chart, giving the sky-chart altitude-circles/azimuth-lines & also a horizon-gradient that looks nice when the chart is black.

Here's the installation-instructions:

* Step1
Place all the included files inside the "Users/Shared/Shared Documents/ACP Web Data/Doc Root/ac/"-Folder

* Step 2
Generate your chart: Create your star chart using the online generator at http://www.fourmilab.ch/cgi-bin/Yoursky
You can decide for your self how many stars and dso's that'll be visible, how many / what names and so on. There are 2 settings that you must set in a specific way, those are listed here:Date and Time : Now (MUST)
Observing site: Coordinates for your observatory/site, be as specific as possible, fields accept ° ' " symbols (MUST)
Remember the image-size you entered, it must be inserted in the user input section inside the skychart.asp

The rest can be altered any way you want, including the size, I prefer to keep the chart relatively simple, since I'm occasionally uses the chart from my phone. Here's the settings I use: